Today, long-haul optical transmission systems typically utilize a continuous wave (CW) laser and a separately mounted lithium-niobate Mach-Zehnder modulator as a transmitter due to the desirable properties of high output extinction ratio of the CW laser and low modulator chirp of the lithium-niobate Mach-Zehnder modulator. Disadvantageously, the use of “separate” components increases board space usage and, therefore, cost. There is currently no adequate compact, low cost integrated CW laser/EA modulator solution that supports the non-return to zero (NRZ) modulation format for long-haul optical transmission. Such integrated CW laser/EA modulator solution that supports the NRZ modulation format for long-haul optical transmission disadvantageously results in low output extinction ratio of the EML and high modulator chirp.
Koch et al. (“Dispersion Compensation by Active Predistorted Signal Synthesis,” Journal of Lightwave Technology, Vol. LT-3, No. 4, August 1985) partially address this EML long-haul optical transmission problem, by predistorting a signal to include the inverse function of the fiber transfer function and modulating the laser, as well as the modulator, to remove the dispersion effect from the transmitted signal. Specifically, Koch et al. present a technique for high bit rate time division multiplexed optical transmission utilizing the synthesis of a predistorted signal to compensate for the dispersion effect. By utilizing dispersion as an integral part of the signal processing, bit rates can be achieved in excess of those at which dispersion otherwise prevents optical transmission.
What is still needed, however, is a compact, low cost integrated CW laser/EA modulator solution that supports the NRZ modulation format for long-haul optical transmission that results in high output extinction ratio of the EML and low modulator chirp.